Lake Pontchartrain carries real risks, but it’s not uniformly dangerous. Whether the lake is safe on any given day depends on bacteria levels, weather conditions, and what you’re doing on or in the water. Millions of people boat, fish, and swim along its shores every year without incident, yet the lake has a well-earned reputation for catching people off guard with sudden storms, poor water quality after heavy rain, and wildlife that demands respect.
Bacteria Levels Fluctuate Weekly
The most common health risk for swimmers is fecal bacteria in the water. The Pontchartrain Conservancy tests shoreline sites weekly and measures levels of Enterococcus, a type of bacteria that signals contamination from sewage or animal waste. The EPA’s safety threshold, called the Beach Action Value, is 70 colony-forming units per 100 milliliters of water. When a testing site exceeds that number, it gets flagged red, meaning swimming is not advised.
These readings can swing dramatically from one week to the next. After heavy rainfall, stormwater runoff flushes sewage overflows, street pollution, and animal waste into the lake, often pushing bacteria counts well above the safe limit along the south shore near New Orleans. A few dry, sunny days can bring those numbers back down. If you plan to swim, check the Pontchartrain Conservancy’s weekly results before you go. Avoid the water for at least 48 to 72 hours after significant rain.
Toxic Algal Blooms
When the Bonnet Carré Spillway opens to divert Mississippi River floodwater into Lake Pontchartrain, a cascade of nutrients floods in with it. That pulse of nitrogen and phosphorus fuels cyanobacteria, sometimes called blue-green algae, which can produce toxins harmful to people and deadly to pets. Previous spillway openings have triggered blooms serious enough to prompt health advisories along public shorelines. NOAA’s coastal science division has monitored these events specifically because of the risk that toxins could reach areas where people wade or let dogs swim.
Blooms typically appear as thick, bright green or blue-green mats on the water’s surface. If you see discolored, soupy-looking water or notice a strong musty smell, stay out. Dogs are especially vulnerable because they drink lake water and lick their fur afterward. Exposure can cause skin rashes, nausea, and respiratory irritation in people, and liver failure in dogs.
Weather Can Turn Fast
Lake Pontchartrain is roughly 40 miles wide and extremely shallow, averaging about 12 to 14 feet deep. That combination makes it one of the more treacherous bodies of water in the Gulf region for boaters. Winds blowing across that wide, open fetch build steep, choppy waves quickly because there’s no deep water to absorb the energy.
Thunderstorm complexes moving through southern Louisiana can produce wind gusts near hurricane strength with almost no warning. A 2021 storm system generated gusts of 54 miles per hour at the New Orleans airport as its leading edge crossed the south shore of the lake, and conditions deteriorated rapidly from there. Behind the initial squall line, tropical-storm-force gusts persisted for at least seven hours, making rescue operations nearly impossible. Water levels can also spike suddenly: that same storm system pushed water nearly three feet above predicted tide levels in nearby Barataria Bay.
For anyone boating or kayaking on the lake, the practical takeaway is that a calm morning can become genuinely life-threatening within 15 to 20 minutes when a storm cell approaches. Always check the forecast before heading out, and carry a marine weather radio or an app that provides real-time radar.
Bull Sharks Enter the Lake Every Summer
Bull sharks are one of the few shark species that tolerate brackish and fresh water, and they treat Lake Pontchartrain as a seasonal nursery. Each summer, as water temperatures rise, large numbers of juvenile bull sharks move into the lake. Most are immature animals, typically four to five feet long, with the occasional six-footer reported. Research by the University of New Orleans’s Pontchartrain Institute for Environmental Sciences captured 18 bull sharks between 2000 and 2003 near Goose Point at the mouth of Bayou Lacombe on the north shore.
The reassuring detail: there has never been a documented shark attack on a human in the Lake Pontchartrain Basin, according to long-running records maintained by researchers. Bull sharks are considered one of the species most potentially dangerous to humans worldwide, so their presence warrants awareness, but the lake’s murky water and the sharks’ focus on fish rather than people have kept encounters from turning into incidents. Avoid swimming at dawn, dusk, or in murky water near bayou mouths, which is where bull sharks tend to concentrate.
Fish Consumption Advisories
Mercury contamination affects some fish species caught in the rivers feeding into Lake Pontchartrain. Louisiana’s Department of Environmental Quality has active advisories for the Bogue Falaya and Tchefuncte Rivers, both of which drain into the lake’s north shore. Women of childbearing age and children under seven should not eat largemouth bass or crappie from these waterways at all, and should limit freshwater drum, spotted bass, or catfish to one meal per month. Other adults and older children are advised to cap largemouth bass and crappie at two meals per month and drum, spotted bass, or catfish at four meals per month.
If you’re fishing the lake itself rather than its tributaries, the advisories may not apply to the exact water you’re in, but mercury accumulates in fish regardless of where you catch them. Larger, older predatory fish carry the highest concentrations. Eating your catch occasionally poses little risk; eating it as a dietary staple could lead to mercury buildup over time, particularly in young children and pregnant women.
Drowning and Undertow Risk
Lake Pontchartrain’s shallow depth gives people a false sense of security. The lake bottom drops off gradually in most places, but soft, silty mud can make it difficult to regain footing if you stumble. Wind-driven currents, especially during afternoon sea breezes or ahead of approaching storms, can push swimmers along the shore or away from shallow areas faster than they realize. The lake doesn’t produce ocean-style rip currents, but the combination of wind, current, and limited visibility in the brown water creates a drowning risk that catches inexperienced swimmers off guard.
Most of the shoreline lacks lifeguards. If you’re swimming with children, stay in areas where you can stand comfortably and keep a close eye on wind shifts. Wearing a life jacket while paddleboarding or kayaking isn’t optional here: conditions that are manageable at launch can change in minutes.